<!doctype html>
<html>
	<head>
		<meta charset="uft-8">
		<title></title>
		<style>
			#d1{
				width:600px;
				/*不写高*/
				/*height:100px;*/
				border:3px solid #f00;
				/*float:left;*/
			}
			#d2,#d3,#d4{
				width:198px;
				height:100px;
				margin-right:2px;
				background:#0ff;
				float:left;
			}
			#d5{
				clear:both;
			}
		</style>
	</head>
	<body>
		<div id="d1">
			<div id="d2"></div>
			<div id="d3"></div>
			<div id="d4"></div>
			<div id="d5"></div>
		</div>
	</body>
</html>